Determination of avidity of IgG to cytomegalovirus in serum by the method of immunochemiluminescence
Cytomegalovirus (CMV) belongs to the herpes virus family. Like other members of this group, it can persist in humans for life.
In healthy people with normal immunity, the primary infection is uncomplicated (and often asymptomatic).
It is known that CMV is a member of the group of TORCH infections, which are potentially dangerous for fetal development and cause severe organ damage in newborn babies.
One of the main ways of immunological protection of the organism is realized in the form of an attack by the host's antibodies against antigens that have entered from outside.
An antigen is a substance that has signs of genetic foreignness. It can be, for example, a fragment of a bacterial wall or a virus capsule.
An antibody is a protein that is made inside immune defense cells and can neutralize an antigen. Scientists distinguish five main classes of antibodies (immunoglobulins).
For the diagnosis of cytomegalovirus lesions, two of them are the most important: IgG and IgM. IgM immunoglobulins appear in the blood first.
Their detection in the bloodstream is a sign of acute infection. As the inflammation subsides, this type of immunologically active proteins disappears from the bloodstream.
Representatives of the IgG class appear later than IgM in the acute phase of infectious invasion. However, after the infection they remain in the blood for a long time, participating in the process of immunologic memory formation.
By analyzing the combinations of immunoglobulin types present in the blood, it is possible to understand whether a person is currently carrying an acute cytomegalovirus infection or whether he or she has had the disease before.
Detection of both types of antibodies in the bloodstream means an acute infectious disease or activation of a chronic infection process. Why is it necessary to detect cytomegalovirus avidity? The fact is that the time period of IgM antibodies in the bloodstream can vary greatly. It is generally believed that IgM circulate in the bloodstream for 3-5 months and then disappear. But there are known cases when they were detected 2 years after the disease was passed.
At the same time, in severe immunodeficiency they may not be present in the blood at all. In such situations, false-positive or false-negative results may be obtained. The avidity assay circumvents this problem and provides more accurate data regarding cytomegalovirus carriage.
This method was introduced into clinical practice in 1989 by Professor Klaus Hedman of the University of Helsinki. Most often the need for this test arises in pregnant women. This is due to the fact that acute cytomegalovirus infection can cause significant harm to the child developing in the womb.
If a pregnant woman is found to have class M antibodies to cytomegalovirus in addition to IgG, there is a serious risk. It is extremely important to find out whether this result is not a false positive. If it is not, it is necessary to clarify whether an acute infection has developed or reactivation of a chronic infection has occurred. The prognosis of the fetus depends on this. Determination of avidity can clarify the situation.